The harmonic balance method (HBM) was originally developed for finding periodic solutions of electronical and mechanical systems under a periodic force, but has later been adapted to self-sustained musical instruments. Unlike time-domain methods, this frequency-domain method does not capture transients and so is not adapted for sound synthesis. However, its independence of time makes it very useful for studying every periodic solution of the model, whether stable or unstable without care of initial conditions. A computer program for solving general problems involving nonlinearly coupled exciter and resonator, Harmbal , has been developed based on the HBM. The method as well as convergence improvements and continuations facilities are thorougly presented and discussed in the present paper. Application of the method is demonstrated on various problems related to a common model of the clarinet: a reed modelled as a simple spring with and without mass and damping, a nonlinear coupling and a cubic simplification of it, and a cylindrical bore with or without dissipation and dispersion as well as a bore formed as a stepped cone.